STUDIES ON THE PHYTOCHEMICAL AND NUTRITIONAL PROPERTIES OF TETRACARPIDIUM CONOPHORUM (BLACK WALNUT) SEEDS

Abstract

This study evaluated the phytochemical, proximate, vitamin and mineral element composition of Tetracarpidium conophorum (black walnut) seeds. The

Full text

Research Paper
STUDIES ON THE PHYTOCHEMICAL AND NUTRITIONAL PROPERTIES
OF TETRACARPIDIUM CONOPHORUM (BLACK WALNUT) SEEDS
Ojobor Charles Chijioke
1
,
Anosike Chioma A.
1
and Ani Chijiokes Collins
2
1
Department of Biochemistry,
University of Nigeria, Nsukka, Nigeria
2
Department of Biological Sciences,
University of Agriculture,
Makurdi, Benue State, Nigeria.
Abstract
This study evaluated the phytochemical, proximate, vitamin and mineral
element composition of Tetracarpidium conophorum (black walnut) seeds. The
proximate analysis of the seed extract revealed 31.40±0.01% moisture;
3.77±0.02% crude fats; 28.85±0.01% crude protein; 6.01±0.02% ash;
8.66±0.02% fibre; 21.30±0.04% carbohydrate. Phytochemical analysis of the
seed extract also revealed the presence of alkaloids 2.29±0.02 mg/100g,
saponins 8.07±0.01mg/100g, flavonoids 0.02±0.02mg/100g, terpenoids, tannins
0.89±0.02mg/100g, glycosides 2.19±0.01mg/100g, reducing sugar
4.10±0.11mg/100g but no resins. The seeds are also rich sources of mineral
elements like calcium 44.99±0.14mg/100g, potassium 24.08±0.25mg/100g,
sodium 9.59±0.08mg/100g, magnesium 59.77±0.78mg/100g, phosphorus
265.92±0.32mg/100g, iron 2.89±0.02, zinc 6.78±0.08mg/100g, manganese
3,20±0.02 mg/100g and copper 1.87±0.02mg/100g. The seeds also contain
some appreciable amount of some vitamins: vitamin A 2.24±0.06mg/100g,
vitamin C 5.08±0.01 and vitamin E 70.00±0.82mg/100g. Other vitamins found in
trace amounts were vitamin D, K, B
1
, B
2
, B
3
, B
5
, B
6
, B
9
and B
12
.
Key words: Black walnut seed, Phytochemical screening, Proximate analysis,
Mineral content, Vitamin analysis.
INTRODUCTION
Tetracarpidium conophorum otherwise known as walnut is an edible seed of the tree which
belongs to the genus juglans and the family juglandaceae. It is a large deciduous tree attaining
the height of 25-35m and a trunk up to 2m diameter with a short trunk and broad crown
(Caglarimark, 2003). It is light-demanding specie, requiring full sun to grow well (Brinkman,
1974). Walnut comprises such families as Juglandaceae (English walnut), Euphorbiaceae and
Olacaceae (African walnut). It is an economic plant widely cultivated for the production of nuts
and it is used as delicacies (Adebona, 1988). The English walnuts are called Juglan regia while
the black walnuts are known as Juglans nigra. Each family has its own peculiar characteristics
but they have some things in common such as the nuts. Tetracarpidium conophorum is known in
the Easthern Nigeria as ukpa (Igbo), Western Nigeria as awusa or asala (Yoruba) and Northern
Nigeria as gawudi bairi (Hausa). It is cultivated principally for its nuts which are cooked and
consumed. Black walnut grows best on moist, deep, fertile, well-drained, loamy soils; although it
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Journal of Global Biosciences Vol. 4(2), 2015 pp. 1366-1372
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also grows quite well in silty clay loam soils (Williams, 1990; Cogliastro et al., 1997). These sites
include coves, bottomlands, abandoned agricultural fields, and rich woodlands. Tetracarpidium
conophorum is known in the littorial and the western Cameroon as kaso or ngak and serves as
an edible nut eaten between meals. The leaf extract of T. conophorum possesses antibacterial
and antifungal activities. The root extract of the plant also displays antibacterial activity
(Ajaiyeoba and Fadare, 2006). Walnuts extract possess anticancer property (Herbert et al.,
1998) and reduce diabetic complications (Kaneto et al., 1999). Also, the presence of oxalates,
phytates, tannins as well as proteins, fibres, oil and carbohydrate in Tetracarpidium conophorum
has been reported (Enujiugha, 2003). The phytochemical and nutrient evaluation of
Tetracarpidium conophorum (Nigerian walnut) root has also been reported (Ayoola et al., 2011).
Therefore, the objective of this work was to evaluate the proximate, phytochemical, mineral and
vitamin constituents of the seed sample of Tetracarpidium conophorum.
MATERIALS AND METHODS
Collection and preparation of plant material: Healthy seeds of walnut were obtained from
Nkwo-Ibagwa, Igbo Eze South L.G.A., Enugu State. The seeds were identified and authenticated
at the Department of Plant Science and Biotechnology, University of Nigeria, Nsukka (UNN). The
freshly collected seeds of Tetracarpidium conophorum were dehulled, chopped, sun-dried to
constant weight, and milled to powder using the hand mill. Portions of the powdered sample
were then used for the various analyses.
Qualitative phytochemistry: Qualitative phytochemical analysis of the samples for alkaloids,
glycosides, saponins, flavonoid, tannins, terpenoid, reducing sugar and soluble carbohydrates
were carried out by methods described by Harborne (1973).
Quantitative phytochemistry: Quantitative phytochemical screening of the samples for
relative abundance or absence of alkaloids, glycosides, saponins, flavonoids, tannins, terpenoid,
reducing sugar and soluble carbohydrates were carried out by method outlined by Pearson
(1976).
Proximate analysis: The proximate analysis of the seed extract for crude protein, crude fiber
and fat contents were determined using the methods described by Pearson (1976). Crude
protein determination was done using Kjedhal’s method, while crude fibre determination was
done using acid and alkaline digestive method. Fat content was determined using continuous
solvent extraction method. Total ash content was determined by ignition at 550
o
C in a muffle
furnace for 4hr. Moisture and carbohydrate contents were determined using the methods
described by AOAC (1990).
Mineral analysis: The methods outlined by AOAC (2000) were used for the determination of
minerals in the test sample. Calcium, sodium, potassium, magnesium were determined by flame
photometric method while iron, zinc, manganese and copper were determined by atomic
absorption spectrophotometric method. The sample (2g) was weighed and put into a clean
dried crucible. Then it was transferred to a muffle furnace, ashed at 700
o
C for 3 hours and
cooled in a dessicator. 30% HCl (5 ml) was added, with 10 ml 0f distilled water and diluted to 50
ml with distilled water. The resulting solution was use in the analysis of iron, zinc, manganese
and copper respectively.
Vitamin analysis: The composition of the water soluble vitamins such as thiamine, niacin,
pantothenic acid, pyridoxine, cobalamin, folate were determined by the method of Association
of Official and Analytical Chemists (AOAC, 1990). Vitamins A, C, D, E and K contents were
determined by the method described by Okwu (2004)
RESULTS AND DISCUSSION
The result obtained from the phytochemical tests Tetracarpidium conophorum seeds. These are
as follows;

Journal of Global Biosciences Vol. 4(2), 2015 pp. 1366-1372
ISSN 2320-1355
http://mutagens.co.in 1368
Table 1: Qualitative Phytochemicals Results of Tetracarpidium conophorum seeds.
Phytochemicals Walnut
Alkaloid +++
Flavonoid +
Saponins +++
Glycoside +++
Tannins +
Soluble Carbohydrate ++
Hydrogen Cyanide ND
Terpenoid
Reducing sugar
ND
+++
KEY: + Trace amount present
++ Moderate amount present
+++ Appreciable amount
ND Not detected.
The qualitative phytochemical constituents of walnut (Tetracarpidium conophorum) are shown
in table 1. Analyses revealed high abundance of alkaloid saponins, glycoside and reducing sugar
in Tetracarpidium conophorum seeds. There were also moderate amounts of soluble
carbohydrate observed in the sample. However, phytochemicals such as flavonoid, and tannins
were observed in trace amounts while hydrogen cyanide and terpenoid were not detected in the
samples.
Table 2: Quantitative Phytochemical results of Tetracarpidium conophorum seeds
Values are means of three Determinations ± S.D.
Table 2 shows the phytonutrients present in the seed sample analysed. The results obtained
from the phytochemical analyses show high concentration of alkaloid (2.29 ± 0.02 mg/100g);
saponin (8.07 ± 0.01 mg/100g); glycoside (2.19 ± 0.01 mg/100g); reducing sugar (4.10 ± 0.11
mg/100g), moderate concentration of soluble carbohydrate (1.06 ± 0.01 mg/100g) and trace
amount of flavonoid (0.02 ± 0.02 mg/100g); tannins (0.89 ± 0.02 mg/100g). Phytochemicals are
biologically active compounds, found in trace amounts, which are not established nutrients but
which nevertheless contribute significantly to protection against degenerative diseases
(Dreosti, 2000). The results of phytochemical analysis revealed appreciable amount of alkaloids,
saponins, glycosides and reducing sugar. However, other phytonutrients were also quantified.
Flavonoids have protective effects including anti-inflammatory, anti-oxidants, antiviral, and
anti-carcinogenic properties. They are generally found in a variety of foods, such as oranges,
Phytochemical
Mean Composition
(mg/100g dry
weight)
Alkaloid (mg/100g) 2.29 ± 0.02
Flavonoid ( mg/100g) 0.02 ± 0.02
Saponins ( mg/100g) 8.07 ± 0.01
Glycoside ( mg/100g) 2.19 ± 0.01
Tannins ( mg/100g) 0.89 ± 0.02
Soluble Carbohydrate(mg/100g) 1.06 ± 0.01
Hydrogen Cyanide (mg/100g) 0.02 ± 0.01
Terpenoid ( mg/100g) 0.01 ± 0.02
Reducing Sugar (mg/100g) 4.10±0.11

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tangerines, berries, apples and onions (Middleton et al., 2000). The presences of tannins in the
sample suggest that it could be used for healing of haemorrhoids and varicose ulcers in herbal
medicine (Igboko, 1983; Maduiyi, 1983). Alkaloids are heterogeneous group of naturally
occurring compounds found in the leaves, bark, roots or seeds of plants. They are the most
effective plant substance used therapeutically as analgesic, antimicrobial and bacterial
properties. This may probably be the reason walnut is believed to stop asthma (not acute
asthma) and also a constipation cure for elderly. However, the high amount of saponins in the
walnut samples is in closed conformity with the earlier report of Ayoola et al., 2011, for walnut
root and it is an indication that walnut has a cytotoxic effect such as permealisation of the
intestine. Saponin also gives the plant its bitter taste; saponin has relationship with sex
hormones like oxytocin. Oxytocin is a sex hormone involved in controlling the onset of labour in
women and the subsequent release of milk (Okwu and Okwu, 2004).
Table 3: Proximate Composition of Tetracarpidium conophorum seeds.
Proximate Mean Composition
Moisture (%) 31.40 ± 0.01
Ash (%) 6.01 ± 0.02
Fats (%) 3.77 ± 0.02
Fibre (%) 8.66 ± 0.02
Protein (%) 28.85 ± 0.01
Carbohydrate (%) 21.30 ± 0.04
Energy Value (kcal) 234.57 ± 0.02
Values are means of three Determinations ± S.D.
Table 3 shows the percentage proximate composition of the samples. The proximate
compositions of Tetracarpidium conophorum seed were moisture (31.40±0.01%), fats
(3.77±0.02%), protein (28.85±0.01%), ash (6.01±0.02%), fibre (8.66±0.02%), carbohydrates
(21.30±0.04%) and energy values (234.57±0.02 kcal) respectively. These values were fairly in
agreement with earlier reports on proximate compositions of these seeds by Ayoola et al., 2011
and Okwu, 2004. The moisture content is an important parameter as it affects the percentage
yield of the seed oils during extraction (Mansor, et al., 2012). This indicates why the walnut seed
has low oil yield judging from the high amount of its moisture content. The fibre and protein
contents of the sample show that it is nutritionally potent and also, could be regarded as
valuable sources of dietary fibre in human nutrition. Adequate intake of dietary fibre can lower
cholesterol level, risk of coronary heart diseases, hypertension, constipation, diabetes, colon and
breast cancer (Ishida et al., 2000; Rao et al., 1998).
Table 4: Mineral Analysis of Tetracarpidium conophorum seeds.
Mineral Elements
Mean Composition
(mg/100g dry weight)
Copper (mg/100g)
1.87 ± 0.02
Manganese (mg/100g) 3.20 ± 0.02
Zinc (mg/100g) 6.78 ± 0.08
Iron (mg/100g) 2.89 ± 0.02
Phosphorus (mg/100g) 265.92 ± 0.32
Magnesium (mg/100g) 59.77 ± 0.78
Calcium (mg/100g) 44.99 ± 0.14
Potassium (mg/100g) 24.08 ± 0.25
Sodium (mg/100g) 9.59 ± 0.08
Values are means of three Determinations ± S.D.

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The results of the mineral constituents of the seeds as shown in Table 4 revealed copper
(1.87±0.02mg/100g), manganese (3.20±0.02mg/100g), zinc (6.78±0.08mg/100g), iron
(2.89±0.02mg/100g), phosphorus (265.92±0.03mg/100g), magnesium (59.77±0.77mg/100g),
calcium (44.99±0.14mg/100g), potassium (24.08±0.25mg/100g) and sodium
(9.59±0.08mg/100g). Our results were found higher when compared with mineral values
reported by Caglarirmak (2003) for English walnut (Juglans regia) kernel. The result indicates
that walnut seeds are rich source of some minerals and it becomes so important when the
usefulness of such nutrients like Ca, Mg, K, Na in the body are considered. The minerals play
important roles in health and nutrition. However, the Na and K content of Tetracarpidium
conophorum is an added advantage because of the direct relationship of sodium intake with
hypertension in human (Dahl, 1972). This could be the reason for earlier report by James, 2000
which states that walnut contains active agent for prevention and control of high blood
pressure. Calcium and phosphorus are very essential for bone metabolism and assist in teeth
development. Calcium is also a cofactor of three important enzymes; pyruvate dehydrogenase
complex, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase complex in the citric
acid cycle. The presence of copper may be responsible for the absorption of iron, it is therefore,
often seen with iron naturally. Copper is also important for cellular defense and protection of
the mucous membrane, antianaemic and essential for the formation of haemoglobin from iron
(Claude and Paule, 1979). Iron plays important roles in many proteins and enzymes, notably in
haemoglobin to prevent anaemia. The amount of Manganese determined on walnut shows that
the plant can be used to protect bone disease (James, 2000). The activity of this element is
noticeable in the metabolism of food incorporated into the bone. Manganese is also necessary
for the functioning of the pituitary gland, the pineal gland and the brain (Claude and Paule,
1979), it promotes hepatorenal function, combat anaemia and also essential for growth. The
amount of zinc found in walnut sample is an indication that the seed may have some effect on
the nerve function and male fertility. It is also important for normal sexual development,
especially for the development of testes and ovaries, it is essential for reproduction. Zinc
stimulates the activity of vitamins, formation of red and white corpuscles (Claude and Paule,
1979), healthy functioning of the heart and normal growth (Elizabeth, 1994). Zinc is also an
antioxidant, as it is a cofactor for many antioxidant enzymes such as glutamate dehydrogenase,
alcohol dehydrogenase, lactate dehydrogenase, DNA and RNA polymerase, superoxide
dismutase etc. Magnesium is a cofactor of many enzymes such as kinases, phospatase,
transketolase, ribonuclease, carboxylase, peptidase and adenylyl cyclase. A good example is
seen in glycolytic pathway were it serves as a cofactor of the enzymes that catalyse steps one,
two, three, seven, eight and ten of the pathway.
Table 5: Vitamins analysis of Tetracarpidium conophorum seeds
Vitamin Mean Composition
(mg/100g dry
weight)
VitaminA 2.24±0.06
VitaminC 5.08±0.01
VitaminD 0.43±0.02
VitaminE 70.00±0.82
VitaminK 0.08±0.01
VitaminB
1
0.20±0.01
VitaminB
2
0.89±0.06
VitaminB
3
0.14±0.01
VitaminB
5
0.02±0.01
VitaminB
6
0.06±0.04
VitaminB
12
0.38±0.02
Folate 0.07±0.01
Values are means of three Determinations ± S.D.

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The results of the vitamins analyses proved that the sample have preponderance amount of
vitamin A (2.24±0.06 mg/100g), vitamin C (5.08±0.00 mg/100g), vitamin E
(70.00±0.08mg/100g) respectively. As a result of the presence of ascorbic acid in both seeds,
the plants can be used in herbal medicine for the treatment of skin conditions, including eczema,
pruritus, psoriasis and parasitic skin conditions (D’Amelio, 1999). This vitamin can also be used
for the treatment of common cold and other diseases like prostate cancer (Okwu and Okwu,
2004; Okwu and Okeke, 2003). There is also an interesting ability of ascorbic acid as an
antioxidant, to prevent or at least minimises the formation of carcinogenic substances from
dietary material (Hunt et al., 1980). Deficiency of ascorbic acid is associated with pains in the
joint and defect in skeletal calcification, anaemia, manifestation of scurvy haemorrhage from
mucous membrane of the mouth and gastrointestinal track (Hunt et al., 1980). Report also
indicates that walnut could be used in treatment of indigestion, constipation and diarrhea
(Ayoola et al., 2011). The vitamin E content of walnut was exceptionally high and this supports
its use in Southern Nigeria ethno-medicine as a male fertility agent (Ajaiyoba and Fadare, 2006).
Other vitamins determined in this work (table 5) though observed in trace amount are essential
for body metabolism.
CONCLUSION
The present study has shown the proximate, vitamins, minerals and phytochemical
compositions of Tetracarpidium conophorum (Nigerian walnut) seed. This partly shows the use
of this seed in herbal medicine. As a rich source of alkaloids, coupled with the presence of the
essential vitamins and minerals, T. conophorum can be seen as a potential source of useful food
and drugs. The presence of tannin supports its anti-inflamatory property. This also proves that
the seed may be helpful in asthma, rheumatoid and arthritis. High content of ascorbic acid also
indicates that the plant can be used to prevent or at least minimize the formation of
carcinogenic substances from dietary material. Further studies have to be carried out to isolate,
characterize and elucidate the structure of the bioactive compounds from the seed for industrial
drug formulation. More so, extensive works should be carried out to search for the effectiveness
of the seed in male reproductive organ and also its cardiovascular functions.
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